Direct
The more recently established direct disperse process for dye sublimation benefits from many of the same material characteristics, including the amorphous areas of the polymers and the lack of aqueous state for the ink particles, but as the name suggests, dispersed inks are directly placed onto the fabric or non-woven substrate. In this sense, it is a one-step process, rather than the two-step transfer process.
One of the main differences is the use of a coated substrate. The coating is essential in preventing the dispersed inks from spreading across the material in an uncontrollable manner, which would ruin the sharpness of the printed graphics.
Transfer-based dye sublimation still achieves better edge sharpness in images, but today’s direct disperse dye sublimation printers have been engineered to a high standard and are certainly adequate for many common applications. By applying large amounts of ink onto the face side of an open and lightweight material, an almost complete print-through effect can be achieved.
This type of printing requires a raster image processor (RIP) software package to prepare the images, a printer designed specifically to work with textile-based substrates (i.e. with tension control, web guiding under the printheads and a tray to collect any ink that passes right through the substrate), the aforementioned coated substrates. The printer may also need to facilitate temperature and time control with an on-board unit, if there is no separate heat press.
The nature of a fabric’s fibres plays a significant role in its print receptivity.
Comparison points
Given these differences, there are many factors to consider and ‘homework’ to do before investing in either transfer-based or direct disperse dye sublimation systems, but the best choice is often dictated by the sign shop’s desired applications.
Flags and banners, for example, may require the ink penetration of direct disperse printing to create a two-sided graphic product. The most common method for producing sportswear, on the other hand, is to work with precut garment sections and undertake transfer-based printing with a hand press or a suitable singe-piece transfer calender.
That said, both processes are feasible for most general graphic applications. The choice may come down to more specific points of comparison, including the customer’s quality requirements, the choice of substrate, in-house production logistics, required investments and combined production costs.
Quality
In some cases, quality requirements vary by installation venue. Edge sharpness, for example, is a more significant parameter for point-of-purchase (POP) displays than for large facility signage.
The customer may set the bar for quality, too. Many big organizations have strictly defined levels of quality control for how their branded graphics appear, whereas a small, local client may be more concerned about the cost-to-benefit ratio of a specific graphic application.
Substrate
Textiles offer unique properties that have proven benefits for the sign industry, but they are not the easiest materials to work with. A stable woven or warp knit material can be processed effectively using a roll-to-roll machine that provides a degree of tension; many printers and ‘fixation’ units fit this description. Less stable materials, on the other hand, can suffer from problems like wrinkling, elongation and width reduction as a result of the application of tension during direct disperse dye sublimation. Some signmakers spend a lot of time to make these less stable fabrics work well, but for the most part, printing onto transfer paper first is the only effective process for them.
Even if a type of material seems to work well, similar textile products from different suppliers may behave completely differently. For one thing, the differences in how textiles have been preprocessed—e.g. thermofixed through the application of both temperature and pressure—are not usually obvious at a glance in a sample book, but will become evident when high temperatures are applied in the sign shop’s rotary calender or a printer’s fixation unit.
Infrared radiation (IR) fixation units and beltless calenders offer no adequate measures to prevent less stable fabrics from shrinking or wrinkling, but calenders equipped with belts do, as the belt holds the material against the heating drum and guides it through the machine without adding further tension. Even then, however, the question remains as to whether or not the printer can cope well with the material. Hence, transfer-based dye sublimation remains the go-to option, as it is perceived as the safest route to take.
In any case, it will require some experience with the processing of textiles before signmakers can make a balanced choice between transfer-based and direct disperse dye sublimation.
